Automatic repeat request (arq) reset method

ABSTRACT

An Automatic Repeat-reQuest (ARQ) Reset method for an ARQ transmitter disables ( 120 ) transmission, starts ( 130 ) an ARQ transmitter window at a first unacknowledged block, and discards ( 140 ) service data units (SDUs) in the ARQ transmitter window having zero blocks in a ‘not-sent’ state. Thus, for all SDUs having no blocks in a ‘not-sent’ state, the blocks in an ‘outstanding’ or ‘waiting-for-retransmission’ state are changed to a ‘discard’ state. Next, the ARQ transmitter sets ( 150 ) the state of all blocks in partially unsent SDUs of the ARQ transmitter window to ‘not-sent.’ So, any remaining blocks in an ‘outstanding,’ ‘waiting-for-transmission’ or ‘discard’ state are changed to ‘not-sent.’ After the ARQ transmitter enables ( 160 ) transmission and ends ( 190 ) the ARQ Reset procedure, the ARQ transmitter will send blocks in the ‘not-sent’ state. This ARQ Reset method avoids retransmitting blocks that might cause duplicate packets at the ARQ receiver, which some protocols cannot handle.

FIELD OF THE DISCLOSURE

This disclosure relates generally to Automatic Repeat-reQuest(ARQ)-enabled transmitters.

BACKGROUND OF THE DISCLOSURE

According to Section 6.3.4.6.2 of IEEE Standard 802.16e (Institute forElectrical and Electronics Engineers Standard for Local and MetropolitanArea Networks, Part 16: Air Interface for Fixed Broadband WirelessAccess Systems, including Amendment 2 and Corrigendum 1), during an ARQReset procedure, all service data units (SDUs) with ARQ blocks in a‘discarded’ state are to be discarded by an ARQ transmitter and allother ARQ blocks retransmitted after the ARQ Reset procedure hascompleted.

From an ARQ transmitter's point of view, an ARQ block may be in one ofthe following four states: not-sent, outstanding, discarded, andwaiting-for-retransmission. Any ARQ block begins in the ARQ transmitteras ‘not-sent.’ After it is sent by the ARQ transmitter, the ARQ blockbecomes ‘outstanding’ for a “retry-timeout” period of time. While ablock is in the ‘outstanding’ state, it is either acknowledged (an ACKis received from the ARQ receiver) and ‘discarded’, or the blocktransitions to ‘waiting-for-retransmission’ after the retry-timeoutexpires or a NACK is received from the ARQ receiver. An ARQ block cantransition from ‘waiting-for-retransmission’ to ‘discarded’ when an ACKmessage for it is received or after a “lifetime-timeout” period hasexpired.

If an ARQ transmitter and its ARQ receiver lose synchronization, eitherthe ARQ transmitter or the ARQ receiver can initiate an ARQ Resetprocedure to restore synchronization. According to FIG. 34 and FIG. 35of IEEE Standard 802.16e, an ARQ transmitter discards SDUs with one ormore blocks in the ‘discarded’ state during the ARQ Reset procedure.Then, SDUs that have no ARQ blocks in the discard state will be sent (orresent).

One consequence of this behavior is that ARQ blocks that were receivedby the ARQ receiver before the ARQ Reset procedure initiated may beresent after the ARQ Reset procedure is complete. In fact, ARQ blocksfor a complete SDU may be resent in accordance with this procedure evenwhen the complete SDU was already received by the ARQ receiver beforethe ARQ Reset procedure started. For example, all the ARQ blocks for anSDU can be in the ‘outstanding’ state because ACKs sent by the ARQreceiver were not received by the ARQ transmitter. Then, these‘outstanding’ ARQ blocks will transition to ‘waiting-for-retransmission’and be resent after the ARQ Reset procedure has completed. In this case,the ARQ receiver will assemble a duplicate SDU and pass it to the higherlayer. Thus, the higher layer receives duplicate packets.

Some higher layer transport protocols, such as Transmission ControlProtocol (TCP) and Real-time Transport Control Protocol (RTCP), usesequence numbers and will be able to detect and discard these duplicatepackets. Other protocols, however, cannot easily detect and discardduplicate packets. For example, Robust Header Compression (ROHC)specifically requires that lower layers not generate duplicate packets.

Thus, there is an opportunity to prevent duplicate packets resultingfrom an ARQ Reset procedure. The various aspects, features andadvantages of the disclosure will become more fully apparent to thosehaving ordinary skill in the art upon careful consideration of thefollowing Drawings and accompanying Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of an ARQ Reset method for an ARQ transmitter.

FIG. 2 shows a sample ARQ window with one ARQ block per SDU both beforeand after an ARQ Reset procedure performed in accordance with FIG. 1.

FIG. 3 shows a sample ARQ window with two ARQ blocks per SDU both beforeand after an ARQ Reset procedure performed in accordance with FIG. 1.

FIG. 4 shows a sample ARQ window with three ARQ blocks per SDU bothbefore and after an ARQ Reset procedure performed in accordance withFIG. 1.

DETAILED DESCRIPTION

The Automatic Repeat-reQuest (ARQ) Reset method for an ARQ transmitterdiscards all service data units (SDUs) after the start of an ARQtransmitter window that have no blocks in the ‘not-sent’ state andchanges the state of all blocks in partially unsent SDUs to ‘not-sent’.When the ARQ Reset procedure is completed, the ARQ transmitter will send(or resend) all the blocks in the ‘not-sent’ state. By discarding SDUshaving all their ARQ blocks in the ‘discard,’ ‘outstanding,’ and‘waiting-for-retransmission’ states, the ARQ Reset method avoidsretransmitting ARQ blocks that might result in duplicate packets at theARQ receiver. This is important because some transport layer protocolscannot handle duplicate packets or experience poor efficiency whendealing with duplicate packets, while most transport layer protocols canhandle lost packets.

FIG. 1 shows a flow chart 100 of an ARQ Reset method for an ARQtransmitter. In step 110, the ARQ Reset procedure starts. An ARQ Resetprocedure can be initiated by either an ARQ transmitter or an ARQreceiver when it notices that it is out of synchronization with itscounterpart. If an ARQ transmitter initiates the ARQ Reset procedure, itnotifies its counterpart ARQ receiver. If an ARQ receiver initiates theARQ Reset procedure, it notifies its counterpart ARQ transmitter. Eitherway, after the ARQ Reset procedure starts, the ARQ transmitter disablestransmission in step 120. Step 130 sets the ARQ_TX_WINDOW_START to zeroin step 130. This means that the ARQ transmitter notes the location ofthe first unacknowledged ARQ block and the ARQ transmitter window startsat that point. An acknowledged ARQ block is in the ‘discard’ state, soan unacknowledged ARQ block is in a ‘outstanding,’‘waiting-for-retransmission,’ or ‘not-sent’ state.

In step 140, the ARQ transmitter considers partial and complete SDUsoccurring after the start of the ARQ transmitter window. An SDU is adata unit received from an adjacent higher layer. An SDU, sometimescalled a ‘packet’ in this context, is reformatted into one or moreblocks for ARQ transmission. If an SDU has associated no blocks in the‘not-sent’ state, then the SDU is discarded. In other words, if all theARQ blocks relating to an SDU are in either the ‘discard,’‘outstanding,’ or ‘waiting-for-retransmission’ state, then the ARQtransmitter changes all the ARQ blocks for that SDU to the ‘discard’state.

In step 150, the ARQ Reset method considers the remaining SDUs after thestart of the ARQ transmitter window. For any SDUs having associated ARQblocks in both a ‘not-sent’ state and another state (i.e., ‘discard,’‘outstanding,’ or ‘waiting-for-retransmission’), the blocks in the otherstate are changed to the ‘not-sent’ state. This allows complete SDUs tobe transmitted after the ARQ Reset procedure finishes. Because an ARQreceiver discards all incomplete SDUs during an ARQ Reset procedure,step 150 does not result in duplicate packets at the ARQ receiver.

Step 160 enables transmission, and step 190 indicates the end of the ARQReset procedure. When the ARQ Reset procedure is completed, the ARQtransmitter sends ‘not-sent’ blocks with new sequence numbers and theARQ receiver receives these blocks, provides ACKs or NACKs, constructsSDUs, and sends them to the higher layers according to general ARQreception methods. Note that there is no change to the ARQ receiver andit continues to operate in accordance with FIG. 34 and FIG. 35 of IEEEStandard 802.16e.

In order to better understand the effect of the ARQ Reset method shownin FIG. 1, FIGS. 2-4 provide examples with regard to varioustransmission streams.

FIG. 2 shows a sample ARQ window 200 with one ARQ block associated withone SDU both before and after an ARQ Reset procedure performed inaccordance with FIG. 1. The number of blocks associated with anyparticular SDU is variable, and there is shown a consistent one blockper SDU in this example only for the sake of simplicity. Row 290illustrates the concept of higher layer protocol SDUs and shows fourSDUs 210, 220, 230, 240 and allows for further SDUs 250 as well as priorSDUs. Row 292 shows current layer protocol ARQ blocks 212, 222, 232,242, 252 along with the states of the associated ARQ blocks immediatelybefore initiating an ARQ Reset procedure. Row 296 shows current layerprotocol ARQ blocks 216, 226, 236, 246, 256 along with the states of theARQ blocks at the completion of the ARQ Reset method shown in FIG. 1.Note that the ARQ blocks 222, 232 that were in the ‘outstanding’ stateprior to the ARQ Reset procedure are in the ‘discard’ state at theconclusion of the ARQ Reset method. By changing the ARQ blocks 222, 232from the ‘outstanding’ state to the ‘discard’ state as shown by ARQblocks 226, 236, the ARQ Reset method of FIG. 1 avoids retransmittingthe complete SDUs 220, 230 after the ARQ Reset procedure is complete. Byavoid the retransmission of complete SDUs 220, 230, which would resultfrom complying with Section 6.3.4.6.2 of IEEE Standard 802.16e, the ARQReset method of FIG. 1 avoids stressing the higher layer with duplicatepackets.

During the ARQ Reset method of FIG. 1, the start of the ARQ transmitterwindow 280 is set at the earliest ARQ block where no acknowledgement hasbeen received from the ARQ receiver. See step 130 in FIG. 1. Thus, theARQ transmitter window starts at the beginning of ARQ block 222, whichis in the ‘outstanding’ state immediately prior to the ARQ Resetprocedure. Because the ARQ transmitter window will start at the earliestblock that is not in the ‘discard’ state, in a different situation itcould have started at an earliest ‘waiting-for-retransmission’ or‘not-sent’ ARQ block.

All the SDUs having no associated ARQ blocks in the ‘not-sent’ state arechanged to the ‘discard’ state. See step 140 in FIG. 1. Because in thisexample each ARQ block is associated with a unique SDU, the SDUs 220,230 with associated ARQ blocks 222, 232 only in an ‘outstanding’ stateafter the start of the ARQ transmitter window 280 are changed to the‘discard’ state. See ARQ blocks 226, 236. Thus, the SDUs 220, 230 arediscarded. The effect of step 140 in FIG. 1 is that SDUs having alltheir ARQ blocks in the ‘discard,’ ‘outstanding,’ or‘waiting-for-retransmission’ states will be discarded.

Next, all the SDUs with at least one ARQ block in the ‘not-sent’ statewill have all their associated ARQ blocks set to the ‘not-sent’ state.See step 150 of FIG. 1. Because in this example each SDU is representedby only one ARQ block, there is no further change to the state of theARQ blocks during the ARQ Reset method and ‘not-sent’ ARQ blocks 242,252 remain in their ‘not-sent’ states as ARQ blocks 246, 256 when theARQ Reset method ends.

When the ARQ Reset procedure is complete, the ARQ transmitter will sendall the ARQ blocks 246, 256 in row 296 that are in the ‘not-sent’ stateand will process ACKs, NACKs, and timeouts in accordance with thegeneral ARQ process. Although the ‘outstanding’ ARQ blocks 222, 232 werenot acknowledged and also were not re-sent after the ARQ Resetprocedure, there is a chance that the ARQ receiver did receive those ARQblocks 222, 232 and was able to reassemble SDUs for delivery to thehigher layer. If one or more of these ‘outstanding’ ARQ blocks 222, 232was not received by the ARQ receiver, the high layer protocol of the ARQreceiver has methods to handle these lost packets.

FIG. 3 shows a sample ARQ window 300 with two ARQ blocks per SDU bothbefore and after an ARQ Reset procedure performed in accordance withFIG. 1. Although each of the three SDUs 310, 320, 330 shown has twoblocks for the sake of simplicity, SDUs can have differing numbers ofblocks. For SDUs having more than one associated ARQ block, step 140 andstep 150 of FIG. 1 have a slightly more complicated effect. Similar toFIG. 2, row 390 illustrates high layer protocol SDUs 310, 320, 330 andallows for further SDUs 350. Row 392 shows current layer protocol ARQblocks 312, 314, 322, 324, 332, 334, 352 along with the states of theARQ blocks before an ARQ Reset procedure has initiated. Row 396 showscurrent layer protocol ARQ blocks 316, 318, 326, 328, 336, 338, 356along with the states of the ARQ blocks at the completion of the ARQReset method shown in FIG. 1.

In this example, several ARQ blocks 314, 322, 324 in an ‘outstanding’state were changed to the ‘discard’ state by the ARQ Reset method ofFIG. 1 while another ARQ block 332 in an ‘outstanding’ state was changedto the ‘not-sent’ state. This is because of the relationship of each‘outstanding’ ARQ block to other blocks of the same SDU. This differsfrom compliance with Section 6.3.4.6.2 of IEEE Standard 802.16e, whichwould have resent ARQ blocks 326, 328 (as well as resent ARQ block 336)and might have resulted in a duplicate packet corresponding to SDU2 320.

The start of the ARQ transmitter window 380 begins where the firstnon-‘discard’ ARQ block begins. See step 130 of FIG. 1. In this example,the ARQ transmitter window 380 starts at the beginning of the first‘outstanding’ ARQ block 314. Next, the ARQ Reset method inspects SDUsand discards all SDUs with zero blocks in the ‘not-sent’ state. See step140 of FIG. 1. In this example, SDU1 310 has no associated blocks in the‘not-sent’ state, so each of the ARQ blocks relating to SDU1 310 arechanged to the ‘discard’ state as shown by ARQ blocks 316, 318. Also,SDU2 320 also has no associated blocks in the ‘not-sent’ state. So‘outstanding’ ARQ blocks 322, 324 are changed to the ‘discard’ state asshown by ARQ blocks 326, 328. There are no further SDUs with zero blocksin a ‘not-sent’ state.

Next, the ARQ Reset method sets the state of all ARQ blocks in partiallyunsent SDUs to ‘not-sent’. See step 150 of FIG. 1. In this example SDU3330 has an associated ARQ block 334 in the ‘not-sent’ state, which meansit is a partially unsent SDU. The ARQ transmitter then changes any otherARQ blocks associated with SDU3 330 to the ‘not-sent’ state. In thiscase, ARQ5 block 332 changes from the ‘outstanding’ state to the‘not-sent’ state as shown by ARQ5 block 336. Further wholly not-sentSDUs 350 remain in the ‘not-sent’ state.

When the ARQ Reset method is complete, the ARQ transmitter sends all theARQ blocks 336, 338, 356 in row 396 that are in the ‘not-sent’ state andwill process ACKs, NACKs, and timeouts in accordance with the generalARQ process. Although the ‘outstanding’ ARQ blocks 314, 322, 324 werenot acknowledged and also not resent after the ARQ Reset procedure, itis possible that the ARQ2 block 314 was received by the ARQ receiver,processed with the acknowledged ARQ1 block 312 into a complete SDU anddelivered to the ARQ receiver's higher layer. Even if the ARQ2 block 314was never received, the ARQ receiver's higher layer can handle themissing packet related to SDU1 310. Additionally, it is also possiblethat both of the ARQ blocks 322, 324 for SDU2 320 were received by theARQ receiver before the ARQ Reset procedure started, and thus thecorresponding SDU was assembled and delivered to the ARQ receiver'shigher layer. Again, even if SDU2 320 was not reconstructed at the ARQreceiver, transport layer protocols can generally handle missingpackets.

On the other hand, the final ‘outstanding’ ARQ block 332 wasretransmitted because the ARQ receiver is directed to discard allincomplete SDUs during an ARQ Reset procedure. See FIG. 34 and FIG. 35of IEEE Standard 802.16e. Thus, resending the ARQ5 block 336 along withpreviously unsent ARQ6 block 338 does not result in a duplicate packetat the ARQ receiver.

FIG. 4 shows a sample ARQ window 400 with three ARQ blocks per SDU bothbefore and after an ARQ Reset procedure performed in accordance withFIG. 1. Row 490 refers to higher layer protocol SDUs 410, 430 andfurther SDUs 450. Note that although SDU1 410 and SDU2 430 each havethree blocks in this example, further SDUs 450 may have a differentnumber of blocks. Row 492 shows the states of the current layer protocolARQ blocks 412, 414, 416, 432, 434, 436 and further ARQ blocks 452 priorto an initiation of an ARQ Reset procedure. Row 496 shows ARQ blocks422, 424, 426, 442, 444, 446 and further ARQ blocks 456 and their statesafter the ARQ Reset method of FIG. 1 has completed.

In this example, the ‘waiting-for-retransmission’ state ARQ block 414and the ‘outstanding’ state ARQ block 416 were both changed to a‘discard’ state by the ARQ Reset method of FIG. 1 because SDU1 410 hadno blocks in the ‘not-sent’ state. The ‘discard’ state ARQ block 432 andthe ‘outstanding’ state ARQ block 434 were both changed to a ‘not-sent’state by the ARQ Resent method of FIG. 1 because SDU2 430 had an ARQblock 436 in the ‘not-sent’ state. This is different from the behaviorspecified in Section 6.3.4.6.2 of IEEE Standard 802.16e, which wouldhave discarded not only ARQ blocks 424, 426 but also ARQ blocks 444,446. Because an ARQ receiver discards all incomplete SDUs during an ARQReset procedure, discarding ARQ blocks 444, 446 in accordance withSection 6.3.4.6.2 of IEEE Standard 802.16e would have guaranteed amissing packet relating to SDU2 430. On the other hand, changing all ofthe blocks relating to SDU2 430 to a ‘not-sent’ state in accordance withFIG. 1 allows the full packet to be received without any chance of itbeing a duplicate.

The start of the ARQ transmitter window 480 begins at the start of ARQ2block 414, which is the first non-‘discard’ ARQ block. See step 130 ofFIG. 1. According to step 140 of FIG. 1, full and partial SDUs in theARQ transmitter window with zero blocks in the ‘not-sent’ state arediscarded. So for this example, SDU1 410 has no blocks in the ‘not-sent’state and ARQ blocks 414, 416 are changed from their former‘waiting-for-retransmission’ and ‘outstanding’ states to ‘discard’ stateARQ blocks 424, 426. ARQ blocks such as ARQ1 block 422 before the startof the ARQ transmission window are already in a ‘discard’ state.

SDU2 430 has an associated ARQ6 block 436 in a ‘not-sent’ state, so step150 of FIG. 1 sets all of the blocks associated with SDU2 430 to a‘not-sent’ state. Thus, ‘discard’ state ARQ4 block 432 changes to‘not-sent’ state ARQ block 442 and ‘outstanding’ state ARQ 5 block 434changes to ‘not-sent’ state ARQ block 444.

When the ARQ Reset method is complete, the ARQ transmitter sends‘not-sent’ ARQ blocks 442, 444, 446, 456 from row 496 and processesACKs, NACKs, and timeouts in accordance with the general ARQ process.Although ARQ blocks 414, 416 were not acknowledged, they may have beenreceived by the ARQ receiver. If one or more of these ARQ blocks 414,416 were not received by the ARQ receiver, the ARQ receiver's high layershould have procedures to handle a missing packet corresponding to SDU1410.

Although there was an ARQ block 432 in a ‘discard’ state between twounacknowledged ARQ blocks 416, 434, this ‘discard’ state ARQ block 432is set to a ‘not-sent’ state by the ARQ Reset method of FIG. 1 becauseit is part of a partially-unsent SDU 430. Then, after the ARQ Resetmethod has completed, the partially-unsent SDU 430 will be sent in itsentirety using ARQ blocks 442, 444, 446. The partial re-sending of SDU430 will not result in a duplicate packet at the ARQ receiver, becausethe ARQ receiver is directed to discard all incomplete SDUs during anARQ Reset procedure.

The ARQ Reset method avoids duplicate packets at the ARQ receiver. Thisis important because certain higher layer transport protocols cannothandle duplicate packets, or experience low efficiency when dealing withduplicate packets, while most all higher layer transport protocols canhandle missing packets. The ARQ Reset method discards SDUs with zeroblocks in the ‘not-sent’ state and changes the state of all ARQ blocksin partially-unsent SDUs to ‘not-sent.’ When the ARQ Reset method iscompleted and the ARQ transmitter returns to normal operation, the ARQtransmitter will send ARQ blocks for complete SDUs that had not beenpreviously transmitted in their entirety. For SDUs that had all theirARQ blocks transmitted at least once prior to the ARQ Reset procedure,the ARQ transmitter will not transmit them again after the ARQ Resetprocedure even if the blocks were ‘outstanding’ or‘waiting-for-retransmission’ at the time of the ARQ Reset initiation.

While this disclosure includes what are considered presently to be thepreferred embodiments and best modes of the invention described in amanner that establishes possession thereof by the inventors and thatenables those of ordinary skill in the art to make and use theinvention, it will be understood and appreciated that there are manyequivalents to the preferred embodiments disclosed herein and thatmodifications and variations may be made without departing from thescope and spirit of the invention, which are to be limited not by thepreferred embodiments but by the appended claims, including anyamendments made during the pendency of this application and allequivalents of those claims as issued.

As understood by those in the art, the ARQ Reset method may beimplemented using a processor that executes computer program code.Embodiments include computer program code containing instructionsembodied in tangible media, such as floppy diskettes, CD-ROMs, harddrives, or any other computer-readable storage medium, wherein, when thecomputer program code is loaded into and executed by a processor, theprocessor becomes an apparatus for practicing the invention.

It is further understood that the use of relational terms such as“first” and “second”, “top” and “bottom”, and the like, if any, are usedsolely to distinguish one from another entity, item, or action withoutnecessarily requiring or implying any actual such relationship or orderbetween such entities, items or actions. Much of the inventivefunctionality and many of the inventive principles are best implementedwith or in software programs or instructions. It is expected that one ofordinary skill, notwithstanding possibly significant effort and manydesign choices motivated by, for example, available time, currenttechnology, and economic considerations, when guided by the concepts andprinciples disclosed herein will be readily capable of generating suchsoftware instructions and programs with minimal experimentation.Therefore, further discussion of such software, if any, will be limitedin the interest of brevity and minimization of any risk of obscuring theprinciples and concepts according to the present invention.

1. An Automatic Repeat-reQuest (ARQ) reset method for an ARQ transmittercomprising: discarding service data units (SDUs) having zero blocks in a‘not-sent’ state; and setting all blocks in partially unsent SDUs to a‘not-sent’ state.
 2. A method according to claim 1 wherein discardingcomprises: changing a state of a block from ‘outstanding’ to ‘discard’.3. A method according to claim 1 wherein discarding comprises: changinga state of a block from ‘waiting-for-retransmission’ to ‘discard’.
 4. Amethod according to claim 1 wherein setting comprises: changing a stateof a block from ‘outstanding’ to ‘not-sent’.
 5. A method according toclaim 1 wherein setting comprises: changing a state of a block from‘waiting-for-retransmission’ to ‘not-sent’.
 6. A method according toclaim 1 further comprising: disabling transmission by the ARQtransmitter before discarding.
 7. A method according to claim 1 furthercomprising: setting an ARQ transmission window to start at a firstunacknowledged block before discarding.
 8. A method according to claim 1further comprising: enabling transmission by the ARQ transmitter aftersetting.
 9. A method according to claim 8 further comprising:transmitting blocks in a ‘not-sent’ state after enabling.
 10. A methodfor an Automatic Repeat-reQuest (ARQ) transmitter comprising: startingan ARQ Reset procedure; disabling transmission of the ARQ transmitter;starting an ARQ transmitter window at a first unacknowledged block;determining if a first block in the ARQ transmitter window is associatedwith a service data unit (SDU) having blocks in only a ‘discard,’‘outstanding,’ or ‘waiting-for-retransmission’ state; and changing thefirst block to a ‘discard’ state if the first block in the ARQtransmitter window is associated with an SDU having blocks in only a‘discard,’ ‘outstanding,’ or ‘waiting-for-retransmission’ state.
 11. Amethod according to claim 10 further comprising: setting the first blockto a ‘not-sent’ state if the first block in the ARQ transmitter windowis associated with an SDU having at least one block in a ‘not-sent’state.
 12. A method according to claim 10 further comprising:determining if a second block in the ARQ transmitter window isassociated with an SDU having blocks in only a ‘discard,’ ‘outstanding,’or ‘waiting-for-retransmission’ state; and changing the second block toa ‘discard’ state if the second block in the ARQ transmitter window isassociated with an SDU having blocks in only a ‘discard,’ ‘outstanding,’or ‘waiting-for-retransmission’ state.
 13. A method according to claim12 further comprising: setting the second block to a ‘not-sent’ state ifthe second block in the ARQ transmitter window is associated with an SDUhaving at least one block in a ‘not-sent’ state.